Types of memory on a Cisco device

Cisco IOS (Internetwork Operating System) is a proprietary operating system that runs on Cisco Systems routers and switches. The core function of Cisco IOS is to enable data communications between network nodes.

Types of memory on a Cisco device :
Cisco devices usually have four types of memory that are being used for different purposes. These four types are:

1. RAM (Random Access memory) -
It is a computer's short-term memory, which it uses to handle all active tasks and apps. None of your programs, files, games, or streams would work without RAM. It is super-fast and temporary data storage space that a computer needs to access right now or in the next few moments.  So, for example, let’s say you want to work with a spreadsheet. When you start Excel, your computer loads the application into RAM. If you load an existing spreadsheet (which is stored on your hard disk), the operating system copies that information into RAM, too. 

Then you can work with Excel, crunching numbers in your usual fashion. In most circumstances, the computer responds super-fast, because RAM is fast. When you’re done with the spreadsheet, you tell Excel to save it — which means that the data gets copied to the hard disk or other long-term storage. (If you forget to save and the power fails, all that work is gone, because RAM is temporary storage.) And when you close the application, the computer operating system takes it out of RAM and clears the deck so that the space is free for you to work on the next thing.

2. ROM (Read-only memory) -
It is a type of storage medium that permanently stores data on personal computers (PCs) and other electronic devices. Unlike the non-volatile memory of a hard drive, it’s difficult and time-consuming to rewrite a ROM chip’s memory. In most cases, it’s impossible to alter integrated circuits, which may mean you can’t update more basic forms of ROM. You may be able to reprogram some modern types of ROM, but only at slow speeds and with special equipment. These hurdles make traditional ROM poorly-suited for functions that require frequent feature updates or are prone to bugs or security issues.

3. Flash memory -
It is a type of non-volatile storage memory that can be written or programmed in units called “Sector” or a “Block.” Flash Memory is EEPROM (Electronically Erasable Programmable Read-Only Memory) means that it can retain its contents when the power supply removed, but whose contents can be quickly erased and rewritten at the byte level by applying a short pulse of higher voltage. This is called flash erasure, hence the name. Flash memory is currently both too expensive and too slow to serve as main memory. It is widely used with car radios, cell phones, digital cameras, PDAs, solid-state drives, tablets, and printers.

4. Non-Volatile Random Access Memory (NVRAM) -
It is a category of Random Access Memory (RAM) that retains stored data even if the power is switched off. NVRAM uses a tiny 24-pin dual inline package (DIP) integrated circuit chip, which helps it to gain the power required to function from the CMOS battery on the motherboard. NVRAM monitors several system parameters, such as Ethernet the MAC address, serial number, date of manufacture, HOSTID, etc. Therefore, NVRAM is a non-volatile memory type that provides the random access facility.